1. Field of the Invention
The present invention relates to a passive seat belt system for automatic fastening/unfastening of seat belt in response to the boarding or alighting of a vehicle occupant, and, more particularly, to a passive seat belt system capable of preventing an overload state of a motor for driving a movable anchor of the seat belt.
2. Related Background Art
In a passive seat belt system in which the seat belt is fastened or unfastened by reciprocating an anchor, attached to said seat belt, by a driving motor between the front end (unfastened state) of a guide rail and the rear end (fastened state) thereof, the anchor may collide with the head, hand or finger of the vechicle occupant during the anchor movement. Since such collision is annoying, it becomes necessary to immediately interrupt or reverse the movement of the anchor. Also, because a locked rotor current continues to flow in the motor in such state, it is necessary to discontinue such unnecessary current to protect the motor itself.
For this reason, in a system proposed for example in the U.S. Pat. No. 3,822,760, an actuator member provided on the motor actuates a normally open switch in the overload state of the motor to control the rotation thereof, but the above-mentioned problems have not been satisfactorily resolved.
Also, a passive seat belt system for controlling the motor output in response to a change in the ambient temperature is disclosed in the U.S. Pat. No. 4,561,677, and system for controlling the motor output in response to the detection of an obstacle are disclosed in the Japanese Patent Publication No. 9766/1979 and in the Japanese Utility Model Registration Laid-open Publication Nos. 117520/1975, 117519/1975, 117521/1975 and 39341/1975, but these systems are still insufficient for overload detection.
The overload detection means of the present invention will be explained by an example of a passive seat belt system in which the anchor moving time is monitored by a timer, and such system is disclosed for example in the Japanese patent application Ser. No. 29034/1986 of the present applicant.